1. Field of the Invention
The invention relates to a brush, in particular a brush for applying a cosmetic product to the keratinous fibers, especially for applying mascara to the eyelashes or a dye to the hair, and to a make-up device comprising this brush, the brush having a substantially plano-concave profile.
2. Description of the Related Art
Conventionally, a brush for applying a cosmetic product generally comprises an elongate core formed by the helical winding of two branches of a metal wire and bristles implanted radially in this core and gripped between these wound branches. Such brushes may be of various shapes and may comprise cut-outs.
If these brushes are used for applying mascara to the eyelashes, such shapes and such cut-outs are provided in order to make it possible to obtain more or less heavy make-up and greater or lesser lengthening and curving of the eyelashes.
The prior art, for example FR-A-2715038, discloses mascara brushes having any shape, a concave notch having been cut out in the brushes over their entire length. Since the bristles of the concave notch are short, they are only slightly wiped off on exit from the reservoir containing the mascara; such brushes give very heavy make-up.
Brushes having the shape of a portion of a torus are also known, these brushes being obtained by twisting the core of a cylindrical brush in an arc of a circle. Such brushes have a convex face, a concave face and two substantially plane faces. Such brushes are not very easy to handle. For example, if the user rotates the stem of such a brush about its axis between her fingers, for example in order to apply a product to the eyelashes, she must continually correct the distance between the brush and the eyelashes. Moreover, it was found that such a brush loaded the eyelashes, but without smoothing them sufficiently. Brushes obtained by twisting the core of a cylindroconical brush in an arc of a circle have the same disadvantages.
Although these conventional brushes give substantially satisfactory results, it is desirable to have brushes making it possible for the brush to take a good hold of the eyelashes in order to ensure effective smoothing of the product, and good separation of each eyelash while loading the eyelashes with product in order to obtain a sophisticated make-up. It is thus an object of the invention to provide a brush which is simple and economical to use in practice.
It is a further object of the invention to provide a brush for applying a cosmetic product which, when used to apply mascara to the eyelashes, makes it possible to obtain make-up which is sophisticated and of high quality, that is to say heavy, but with the eyelashes appreciably lengthened and well-separated, the brush, moreover, being very easy to handle.
According to a first aspect of the invention, the brush comprises a straight stem defining a main axis, a flexible core comprising two ends, the core being integral with this stem by means of its first end, and bristles implanted radially in this core, the ends of the bristles defining the surface of the brush, this surface comprising a first face. The intersection of any plane passing through the main axis, called the meridian plane, with the surface of the brush defines two curves, called peak lines, having a certain curvature. The peak lines are concave and the first face is substantially straight and parallel to the main axis.
By concave peak lines it is meant that their concavity faces the outside of the brush. The curvature of a peak line is the reciprocal: 1/r of its radius of curvature r.
At each point of the core, the intersection of the surface of the brush with any plane perpendicular to the core defines a cross-section of the brush. Preferably, the core is central in relation to each cross-section of the brush.
The faces are longitudinal portions of the surface of the brush. Preferably, the surface of the brush comprises at least one second face, called a face of maximum curvature. The curvature of the peak lines passes through a maximum in the region of this second face. More preferably, the curvature of the peak lines passes through a single maximum. Preferably, the surface of the brush comprises a single straight face. Preferably, the curvature of the peak lines increases continuously from the straight face to the face of maximum curvature. Preferably, the face of maximum curvature and the straight face are diametrically opposite one another with respect to the core. Preferably, the bristles of the same cross-section are all of the same length.
According to a second aspect of the invention, in a method for the manufacture of a brush according to the invention, a starting brush comprises a straight stem defining a main axis and a flexible core comprising a first and a second end, the first end being integral with this stem, the core being straight and in alignment with the stem, bristles being implanted radially in this core, the ends of the bristles defining the surface of the starting brush, the surface being of overall concave shape, such as, for example, a brush having the shape of a diabolo or of a peanut, the intersection of any meridian plane passing through the main axis, with the surface of the starting brush defining two concave meridian lines having a specific curvature. A first step involves imparting a twist to the core in a meridian plane, the twist being a curvature substantially equal to the curvature of one of the two meridian lines of this plane and being in the opposite direction to the curvature of this meridian line.
At each point of the core, the intersection of the surface of the starting brush with any plane perpendicular to the core defines a cross-section of the starting brush. Preferably, the starting brush is selected in such a way that the core is central in each cross-section of the starting brush.
The surface of the starting brush is thus modified such that one meridian line is converted into a substantially straight peak line, and the curvature of the second meridian line belonging to the same meridian plane is increased substantially. The core remains central in each cross-section of the brush, but these cross-sections are no longer parallel.
Preferably, in a second step, a twist is imparted to that end of the core which is integral with the stem, in order to align the second end of the core with the main axis. The brush according to the invention may thus be used with a mascara reservoir equipped with a wiper of conventional design.
Preferably, one of the meridian planes of the surface of the starting brush is a plane of symmetry of the starting brush. If appropriate, the starting brush has a plane of symmetry perpendicular to the axis of the core. Even more preferably, the surface of this starting brush is a surface of revolution. Advantageously, each cross-section of the starting brush is convex.
This brush is perfectly suitable for making up the eyelashes, and therefore another aspect of the invention provides a make-up device comprising a mascara reservoir and a member for the application of mascara, this application member being a brush according to the invention.
The brush according to the invention has a continuous evolute profile which is plano-concave in relation to its main axis. When the brush executes a revolution about its main axis, for example when the user rotates the stem of the brush between her fingers, it evolves from a substantially plane face which surrounds the straight peak line parallel to the main axis, towards a concave face of increasing radius of curvature, to reach maximum curvature, and then decreasing to return to a plane face.
The substantially plane profile is preferably located diametrically opposite the concavity of the brush with respect to the core. Since each cross-section is perpendicular to the core at any point along the core, the bristles of the brush have a density lower than the rest of the brush along this plane profile. Moreover, these bristles diverge. Preferably, the face diametrically opposite the straight face with respect to the core is that having the greatest curvature. This face thus has a much higher bristle density and these bristles converge.
When the user uses this brush in order to apply a make-up product to the eyelashes, she extracts the brush from the product reservoir, and in doing so passes the brush through a wiper. If the bristles in the same cross-section are all of the same length, they are all wiped. However, the face comprising a substantially plane profile is wiped to a lesser extent because the bristles diverge and are not very dense. By contrast, the face having the greatest curvature is wiped to hardly any extent, since the distribution of the bristles is very dense. The user places the brush against the eyelashes and rotates it between her fingers: the brush smooths, curves and separates the eyelashes by means of its plane profile, then loads the eyelash with product by means of the rest of its surface. The make-up obtained is heavy, lengthened and curved.
Furthermore, the bristles of a brush according to the invention may be of any type: they may be bristles of different lengths, of different diameters or different cross-sections and of different materials, bristles with tapered ends, fork-shaped ends or ends in the form of a pinhead or bristles which have undergone any kind of treatment known in the art.
There may also be provision for the brush according to the first aspect of the invention to comprise an alternation of rows of short bristles and of long bristles, the long bristles alone being taken into account for defining the surface of the brush. This makes it possible to increase the loading of the eyelid with product.
The helical winding of the two branches of the metal wire forming the core may be provided so as to have a right-hand pitch as is conventionally provided in the manufacture of make-up brushes, or a left-hand pitch as taught by FR-A-27011098. To manufacture a brush with a left-hand pitch, the branches of the core are twisted by rotating them to the left in order to form turns which rotate clockwise around the core, starting from the stem and advancing towards the end of the brush. The brush with a left-hand pitch is preferred for the production of brushes according to the invention. This gives the bristle turns an orientation which makes it possible to separate the eyelashes more effectively during make-up.